Idiopathic pulmonary fibrosis (IPF) is a scarring disorder of the lungs with a 3-yr median survival despite the best available treatment. Many mechanistic and small observational studies in humans implicate abnormalities in the coagulation-fibrinolytic systems in the causation of human and experimental pulmonary fibrosis. Collectively, they demonstrate that tissue factor-dependent pro-coagulant activity is induced, and that the normal fibrinolytic activity is suppressed in the alveolar compartment of the fibrotic lung. Despite this conceptual knowledge, there is much to be learned regarding whether factors in the coagulation/fibrinolysis pathways predict prognosis, or anticoagulant treatment response in IPF. In support of the importance of further study of the blood coagulation/fibrinolysis system, patients with IPF have an increased risk of atherothrombosis-related clinical events, and one small trial demonstrates, for the first time, a survival benefit of anticoagulant treatment in IPF. Here, we show preliminary data that there is activation of coagulation (increased tissue factor antigen), and inhibition of fibrinolysis (increased PAI-1 antigen) in plasma from patients with IPF. Strikingly, tissue factor antigen varied as a function of the pulmonary physiologic impairment, consistent with the possibility that prognosis may be reflected in the extent of coagulation activation. Furthermore, plasma fibrin D dimer levels from a small anti-coagulant trial were increased during an acute exacerbation, and those with elevated plasma D dimer levels, despite anticoagulant treatment, were less likely to survive. Our early results indicate that it is feasible to utilize gene expression profiling to identify progression related genes in IPF. Based on the collective data, we hypothesize that abnormalities in the coagulation/fibrinolytic system underlie the pathogenesis of IPF. We propose to test this hypothesis by linking to the NHLBI IPFnet clinical research network Warfarin trial (ACE; Anticoagulant Effectiveness in IPF). ACE is a randomized, double-blind placebo-controlled, multi-center US trial to evaluate the efficacy of Warfarin on outcome in patients with IPF. This parent trial will rigorously determine if Warfarin has an ameliorative effect on IPF. Importantly, it also provides a unique opportunity to evaluate our hypothesis in the context of progression, and response to anticoagulant treatment, in a carefully and thoroughly characterized cohort of IPF patients. The proposed studies are time-sensitive in that they would collect and analyze plasma samples from patients enrolled in ongoing IPFnet trials, at baseline and at timed points thereafter, using handling/processing procedures that are time-sensitive. The IPFnet steering committee recognizes the value of these mechanistic studies and fully supports this application. When completed, we will identify the molecular links, and determine the prognostic significance, of blood coagulation/fibrinolysis to the pathogenesis of IPF. Furthermore, the results will provide the anti-coagulant biological response data to support the linked ACE parent clinical outcome trial, and inform the trial as to mechanism(s) of Warfarin's effect. Identification of the critical molecules in these pathways will also support the future development of more targeted anti-coagulant agents.